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March 2010 | Volume 13 / Number 3
Next Wave Redux

An Alternate Path to Global VoIP Interconnection

Internet telephony has made great strides, but only as islands of VoIP interconnected via the PSTN. VoIP technology cuts costs (e.g. long-distance or enterprise communications), but in a PSTN context. Thus VoIP advantages, like HD voice quality, are lost in the real world. Many solutions have been put forward, but none have gained significant traction.

A new approach, ViPR, is likely to succeed where previous schemes have failed. ViPR stands for the really awkward phrase: verification involving PSTN reachability.

ViPR bypasses the problems that have prevented large-scale federation of otherwise independent VoIP islands. VoIP islands are able to interface externally using either PSTN or SIP protocols. What’s been lacking is an acceptable SIP federation scheme. SIP domain routing couldn’t handle phone numbers, yet phone numbers are ubiquitous and some VoIP devices only have number pads.

ENUM was supposed to solve this by allowing phone numbers to be inserted into the domain name system. Unfortunately, public ENUM requires a chain of control that starts with the ITU-T and follows down to the operators that control each PSTN number block. There are too many entities and most have no incentive to participate, so, no public ENUM. Private ENUM schemes have been just that — private. Whether any could be scaled to serve the planet is unlikely but unknown as none have gained significant market share.

ViPR works with PSTN numbers. It’s completely distributed (no central database, no central authority). It’s highly scaleable. And it incorporates robust security and PSTN-level protection against spam. The protocol details were published in late 2009 in a set of IETF drafts authored by Jonathan Rosenberg and Cullen Jennings (News - Alert), both of Cisco (although Jonathan recently went to work at Skype).

How does it work? Those using ViPR store their phone numbers in a distributed peer-to-peer database. This is indefinitely scalable. Of course there is no proof this data is really true. ViPR leverages the PSTN to confirm who really owns specific PSTN numbers. The first call between any two endpoints is completed over the PSTN. As only the ViPR devices at either end know the details of this call, they use their knowledge to establish secure communications over the Internet and exchange credentials, which are used for subsequent calls (over the Internet). Elegant!

Cisco (News - Alert) is supporting this protocol in its latest Communications Manager release (v.8.0). I’m sure there will be more action within the IETF, and we still need a second vendor to join (could that be Skype (News - Alert)?), but ViPR can work both technically and politically. Expect second vendor support in 2010 and a tipping point two to three years thereafter. IT

Brough Turner (News - Alert) is co-founder of Ashtonbrooke Corp. (, a stealth-mode startup involved in wireless infrastructure.

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